Linda Lavin on her game in 'Our Mother's Brief Affair'

No one does difficult moms like Linda Lavin. The Tony winner and ex-“Alice” star is on her game playing yet another one on Broadway in “Our Mother’s Brief Affair.”

With signature style, wry wit and an irresistible glint in her eye, Lavin makes Anna Cantor, “an average situational liar,” as she’s called, a force to be reckoned with. Lavin can do that in her sleep.

Even so, the play is a snooze.

Too bad, since author Richard Greenberg, a Tony winner for the baseball play “Take Me Out,” gets right to the point in this meditation on identity, as a son and daughter come to terms with the fact that Mom may really be dying this time.

The play’s first line: “Who was she?”

It’s a good question — and a big one. It’s the one that Seth (Greg Keller), Anna’s son, an obituary writer, asks about the widowed mom who raised him and his sib on Long Island. His twin sister, Abby (Kate Arrington), who runs a library in California, tries to help answer it.

Anna, near death and in a fog of Alzheimer’s, blows her kids’ minds with a decades-old secret. She confesses to a short, sweet dalliance in the early ‘70s with Phil (John Procaccino). Anna played around while a teenaged Seth took music lessons at Juilliard.

Linda Lavin plays “an average situational liar.”

Played out in flashbacks, those scenes contain a bombshell reveal of their own. As if to underline the theme of the slipperiness of really knowing a person, Anna’s lover tells her, “I’m not who you think I am.” Turns out he’s a peripheral figure from a famous ‘50s scandal who became the face of betrayal.

Anna should be repelled. But no. She sees him as a kindred spirit due to a past transgression of her own.

Did it happen? Is she making her life story more fascinating — and worthy of an obit by Seth? Who knows.

Greenberg writes sharp and smart dialogue. Lynne Meadow is an efficient director. The cast is fine, but can only do so much with a script that is undercooked and overwritten at the same time. In a narrative trick, the kids take up the telling of Anna’s story — including details they couldn’t know. The fantasy feel that produces is one of the more interesting facets of the play. But too much playing directly to the audience is a trying tool.

The notion of how much we can ever truly know people in our lives is worth exploring. Who was she, indeed? But the question “Brief Affair” leaves you with is “What was that?”